It was 1971, and trash companies were angling for a lucrative prize: a new round of contracts with Boston. A representative from one outfit, eager to bolster its chances, spoke with a friend of Mayor Kevin White, who suggested that a contribution to White’s upcoming campaign would “be a good move.” The contract, the friend added, did not have to go to the lowest bidder.

When the individual met with White in his City Hall office, according to allegations detailed in the former mayor’s newly released FBI file, he allegedly gave White an envelope with $5,000 cash and a promise of $5,000 more.

White took the money, the individual told FBI investigators, and noted that other contractors had not done the “right thing.” Calling them “sons of bitches,” White vowed that he would “fix them.”

White was never charged with wrongdoing. But the allegations, which spurred a 1975 FBI inquiry into alleged bid-rigging by the White administration, emerged in new detail Wednesday after MuckRock, a website devoted to open records, posted White’s FBI file.

The group, which is independent but works in The Boston Globe’s media lab, received the 500-page file after lodging a public records request in February. White, who served as mayor from 1968 to 1984 and is credited with leading the city through the school busing crisis, died in January at age 82.

White’s administration was the target of a wide-ranging federal corruption investigation, and the FBI file details ­inquiries on several fronts.

The FBI also looked into claims that White pressured the John Hancock life insurance company into donating more than $4 million to Boston University in exchange for changing a development agreement with the city, and that he misused his office in a dispute with the City Council. Several lesser claims were also explored.

The documents are often heavily redacted, and most names are blocked out. They feature source testimony, internal memos, handwritten notes, and copies of newspaper stories. They span more than a ­decade, from the launch of the bid-rigging inquiry in 1975 to the conclusion of the Hancock investigation in 1987, when the US attorney’s office declined to prosecute “due to a lack of evidence to substantiate and prove a federal violation.”

Much of the file is devoted to the alleged payoff scheme, which came to light in the press in the mid-1970s. At the time, White denied wrongdoing and said he had been vindicated by an FBI inquiry.

In the dossier, FBI officials wrote that the US attorney’s ­office in Boston was “extremely reluctant” to investigate the claims “in absence of specifics that would develop prosecutable violation.”

In a memo to the FBI director, an investigator wrote that federal prosecutors felt the evidence was “not solid enough” to proceed without “possibly harming White’s chances in the forthcoming mayoralty campaign and a possibility of White’s obtaining a slot on the national Democratic ticket.”

White was considered a contender for vice president in 1972.

Prosecutors who worked in the US attorney’s office in ­Boston during that era could not be reached for comment. White’s lawyer at the time also could not be reached.

Lawrence DiCara, a Boston city councilor through most of the 1970s, said he was unaware of the allegations detailed in White’s file. But he noted that authorities did not file charges, much less prove them, and doubted that the allegations would alter his legacy.

“Had charges been filed, it might have been different,” he said. “But there obviously was not enough evidence. History will still be good to Kevin White for a host of reasons.”

DiCara noted that at the time, the limit for campaign contributions was far higher, and the FBI memo noted that a Sanitas official considered the payments to White as political contributions, rather than ­direct bribes, and that campaign records from 1971 had been destroyed, as was legal at the time. Investigators later noted “wide discrepancies” ­between the testimony of two witnesses to the alleged payoff.

But a representative of ­Sanitas “readily acknowledged” to the FBI that the firm paid $10,000 to White at his request. In a 1977 memo, a Sanitas representative claimed that when he met with White at his office, White said he needed money and asked for “ten big ones.”

Sanitas Waste of Massachusetts received a contract that included an additional $150,000 in profit, the documents allege. “Anyone knowledgeable in the disposal business reviewing the prices should have known the bids contained unusual profit factors,” a 1975 memo stated.

In a report on the John ­Hancock investigation in 1986, the agency described a meeting where White was said to have taken a piece of paper from his pocket and handed it to company representatives. He had written “$4.0,” to indicate that $4 million was the acceptable ­donation, the report stated.

In 1983, Hancock gave $4.5 million to BU, the largest contribution it had ever made to a university. A representative told the FBI the money was not a contribution, but “an expense.”